Electric telephone



(NoModeL.) i

T. T. PROSSER 8v J- P. FREEMAN. v

` 'ELEOTRIG TELEPHUNE. N 0 257,610. Patentedfmay 9,1882.

N. PETERS. Phola-Liihogmphof. Washington. D. C.

UNITED STATES PATENT OFFICE.

TREAT T. PROSSER AND JAMES P. FREEMAN, OF CHICAGO, ILLINOIS; SAID FREEMAN ASSIGNOR TO THE HCME TELEPHONE COMPANY, OF ILLIN CIS.

.ELECTRIC TELEPHONE.

SPECIFICATION forming part of Letters Patent N 0.`257,610, dated May 9, 1882.

Application filedJu1y21,1881. (Nomodel.)

To all whom it may concern.

Be it known that we, TREAT T. IEossEa and JAMES I. FREEMAN, citizens of the United States, residing at Chicago, in the county of Cook and State ot' Illinois, have invented certain new and useful Improvements in Electric Te1ephones5andwe do hereby declare the following to be a full, clear, and exact description ot' the invention, such as will enable others 1o skilled in the art to which itappertaius to make and use the same, reference being had to the accompanying drawings, and to the letters or figures ot' reference marked thereon, which form a part of this specification.

This invention relates to electric telephones adapted to the transmission and reproduction et articulate speech by means of electrical im-` pulses or waves traversing a circuit.

Our improvement (shown in connection with zo an instrument more particularly intended for use as areceiver) consists in constructing the vibrating diaphragm with a central hemispherical depression, the convex side ot' which faces the permanent bar-magnet, and is ar- 2 5 ranged to be in close proximity to the end thereof'. The eii'ect ot' this construction is that the articulation ot' the instrumentclosely resembles natural speech, which it reproduces in a full tone ot' considerable volume.

In order that oni` invention may be clearly understood, we have illustrated in the annexed drawings and will proceed to describe the i:best form thereof at present known to us.

Figure l is a side elevation ot' a telephonie vinstrument embodying our improvement. Fig.

2 is an axial section of the same. Fig. 3 is anedge view ot' our improved vibrating' diaphragm. z

The same letters of reference indicate like 4o parts in all the figures.

The different parts ot' the instrument are mounted on a tubular body, A, of wood,v vulcanized rubber, or other suitable material. The head a of this tube is covered Aby the vibrating diaphragm B, the ilat annulus b of which is confined around its periphery between a shoulder, a', on the head a, and a similar shoulder, c', on Vthe cap C, which is screwed upon the head and covers theA dia- 5o phragm, heilig provided with the usual ceu tral orifice, c,`a.nd the outwardly-flarin g mouth. The central portion of the diaphragm is depressed, so as to form a hollow hemisphere,

b', under the-orifice c ofthe cap C. The diaphragm may be struck up into form; but we tind it to be very perfect in action when it is made ot' a flat annulus, to the inner edge of which the base of the hollow hemisphere is soldered or brazed. We have constructed some of these diaphragme in which the area ot the 6o base planeot' the hemisphere is about onethird ofthe area ofthe dat aunulus, and have found them to act admirably; but this proportion may be considerably varied. The hemisphcrical portion b ot' the diaphragm extends 65 into a chamber formed in the head a., and is in close proximity to one end ot the permanent bar-magnet D, the other end otl which is supported by a screw, d, swiveled in the cover Al on the other end of the body of the 7o instrument. Thus by turning` the screw d the permanent magnet l) may be adjusted to the proper point with reference to the diaphragm. The upper end of the permanent magnet is surrounded by a helix, E, the ends ot' which 75 are in electrical connection with the respective binding-screws F and G, to which the conducting line-wires are to be attached.

The depression b of the diaphragm need not be exactly hemispherical, although we have 8o obtained excellent results `with that form.

\Ve do not claim a diaphraginthc entire vibratory surface of which is 'concavoconvex. rI'he experimental luse ot' such a diaphragm led to the invention of the hereiubet'ore-de- 85 scribed diaphragm, which, for receiving purposes at least, yielded far superior results.

Having thus described our invention, what we claim is 1. A telephonie instrumentconstructed with 9o a diaphragm the unsupported vibratory area of which is composed ot' a tiat annulus and a central hemispherical depression, substantially as before set forth.

2. The combination, substantially as before set i'orth, ot'. the helix, the permanent magnet, and the diaphragm whose unsupported vibratory area is composed ot' a tint annulus and a heinispherical depression.

In testimony whereof we afx our signatures roo in presence ot' two witnesses.

TREAT T. PROSSER. JAMES P. FREEMAN. Witnesses:

F. SEIPPEL, EDWARD G. WALLER. 

